Fixtures for electrochemical processes

ABSTRACT

A rack for use in electroplating having current-carrying metal workpiece mounting brackets which are substantially covered with insulation but which have selected areas not covered with insulation so as to expose the bare metal of the brackets to the surrounding plating solution or air in order to provide efficient transfer of heat from the bracket to the surrounding medium.

United States Patent Wild [54] FIXTURES FOR ELECTROCHEMICAL PROCESSES [72] Inventor: Robert G. Wild, Fraser, Mich.

[73] Assignee: Michael Ladney, Jr., Grosse Pointe Shores, Mich.

[22] Filed: June 3, 1970 [21] App1.No.: 43,149

[52] U.S. Cl. ..204/297 R, 204/286 [51] Int. Cl ..C23b 5/70, B01 r 3/04 [58] Field of Search ..204/297 R, 286-290 [56] References Cited UNITED STATES PATENTS 2,115,616 4/1938 Brown ..204/297 R X 3,042,604 7/1962 Belke ..204/297 R [151 3,655,549 [451 Apr. 11, 1972 1,010,647 12/1911 Leffel ..204/297 R 2,999,802 9/ 1961 Gault ..204/297 R FOREIGN PATENTS OR APPLICATIONS 350,072 1931 Great Britain ..204/297 R Primary Examiner-John H. Mack Assistant Examiner-Regan J. Fay Attorney-Bames, Kisselle, Raisch & Choate [57] ABSTRACT A rack for use in electroplating having current-carrying metal workpiece mounting brackets which are substantially covered with insulation but which have selected areas not covered with insulation so as to expose the bare metal of the brackets to the surrounding plating solution or air in order to provide efficient transfer of heat from the bracket to the surrounding medium.

4 Claims, 4 Drawing Figures FIXTURES FOR ELECTROCHEMICAL PROCESSES This invention relates to improvements in electrochemical process fixtures and more specifically to fixtures which are used for holding workpieces in an electrochemical process such as electroplating.

By way of example, the invention is described in connection with electroplating, although it has utility in other types of electrochemical processes. The electroplating process is a particular type of electrochemical process in which electric current is passed between two electrodes which are either totally or partially submerged in an electrolyte solution. The two electrodes are an anode and a cathode, respectively, and the electrolyte solution is a plating solution. As the electric current passes through the plating solution between the anode and cathode, metal ions are removed from the solution and deposited as molecules on the cathode. In the customary plating process, it is desired to plate a workpiece, and it is therefore necessary that the workpiece should effectively become the cathode. This is accomplished by attaching the workpiece to a fixture and then placing the workpiece and fixture in the electrolyte solution. When electric current is now passed between the anode and the cathode, plating metal is deposited upon the work, thereby accomplishing the desired result. However, in this process, plating metal is also deposited upon the work-holding fixture (normally called a plating rack), and this results in an inefficient and wasteful process. To overcome this undesired result, it has been customary to coat almost the entire work-holding fixture with a suitable insulating material such as plastisol. Since electric current is unable to flow through the insulator, plating will not occur wherever the insulator covers the fixture. In order to maintain the circuit for the flow of plating current, the fixture is not insulated where it contacts the workpiece.

While the use of insulation helps to overcome the excessive plating of the fixture, it gives rise to other significant difiiculties. Although the insulation serves to electrically insulate the fixture, it also thermally insulates the fixture. Heat generated by the flow of plating current through the fixture is not readily transferred through the insulator and its build-up within the fixture causes deterioration and breakdown of the insulation. One cause of this condition is a poor electrical connection between the fixture and the work piece. This poor connection causes higher flow of electric current in the remaining connections and the generation of excessive heat in those fewer components conducting the current load. This problem can be controlled to some extent by greatly oversizing the currentcarrying components, or by installing a quantity of currentcarrying components significantly in excess of the calculated requirements, or by using a more conductive but less desirable metal in the fixture construction.

It is an object of this invention to accomplish efficient treatment of workpieces in an electrochemical process at a minimum fixture cost.

It is a further object of this invention to provide excellent fixture life by preventing the deterioration and breakdown of insulation on the fixture.

It is an object of this invention to provide a work-supporting fixture for use in an electrochemical process which is substantially but selectively insulated and to which workpieces may be detachably mounted.

It is a further object of this invention to provide a work-support fixture which is substantially but selectively insulated so as to provide exposed areas for heat transfer and to provide for minimum plating of these exposed areas.

The invention is more fully explained hereinafter with reference to the accompanying drawings in which:

FIG. 1 shows an electroplating tank with a plating rack therein embodying the present invention.

FIG. 2 is a sectional view taken along the line IIII in FIG. 1.

FIG. 3 is an enlarged fragmentary sectional view taken along the line IIIIII in FIG. 2.

FIG. 4 is a fragmentary sectional view taken along the line IVIV in FIG. 1.

While the invention is applicable to various electrochemical processes requiring workpieces to be supported by an electrode, its use in electroplating is of particular advantage. Accordingly, merely by way of example, the invention is disclosed in connection with an electroplating process.

Referring now to the accompanying drawings and more particularly to FIG. 1, an electroplating tank 10 is shown containing a plating solution 12. Partially submerged into solution 12 are an anode l4 and a plating rack 16. Anode 14 includes a bar 17 and a support hook 18 by means of which the anode is suspended from a rod or bus bar 20 connected to a source of electric current.

Rack 16 includes a frame 22 provided with a pair of support hooks 24 by means of which the rack is suspended from a rod or bus bar 25. A first work-support bracket 26 and a second work-support bracket 28 are mounted on frame 22. Bracket 26 is a non-flexible rod rigidly mounted on frame 22. Bracket 28 is preferably a spring mounted on frame 22 by means of nut 30 and bolt 32, as is clearly shown in FIG. 3. A workpiece 34 is detachably mounted on rack 16 by means of brackets 26 and 28. In the embodiment shown in FIG. 1, frame 22 is completely covered with suitable insulation material, as is work-support bracket 26. Work-support bracket 28 is selectively insulated, as will be discussed hereinafter.

Referring now to FIG. 3, it can be seen that work-support bracket 28 is formed of base metal 36 (preferably a stainless steel spring strip) covered selectively by insulating material 38. In actual practice, either the bracket may be completely covered with insulating material and then insulation may be selectively removed, or the selected portions of the bracket may be masked off before the insulation is applied.

In operation, plating current is conducted from rod 25 through hooks 24 down through frame 22 to work-support bracket 28. The current in said work-support bracket passes through the base metal 36 to the work 34 and then continues through solution 12 to anode l4 and rod 20. The plating current causes metal from the plating solution to be deposited on the work 34, thereby plating the work.

Insulation is removed or omitted from work-support bracket 28 at small selected areas designated 40, 42, 44 and 46. This permits the heat generated by the plating current passing through the work-support bracket to be removed from the bracket at the exposed portions thereof, either by conduction or convection. This prevents the overheating of the worksupport bracket and the resulting deterioration of the insulation thereon. For example, at locations 40 and 42, heat from the bracket will be transferred to the air; while at locations 44 and 46, heat will be given up to the electrolyte solution. It is not necessary that the insulation be removed so as to provide some heat transfer to the air and some to the solution. Insulation may be removed or omitted from selected areas of bracket 28 so as to transfer heat to only the air or only the solution or to both. Insulation is preferably removed or omitted from the work-support bracket at locations which are further distant from anode 14 than is the work 34, and these locations are preferably so disposed as to face away from anode 14. Thus as shown in FIG. 1 the bare areas 40, 42, 44 and 46 are on the shaded side of bracket 28 relative to anode 14. In this way, the plating of these exposed areas is reduced to a very minimum.

The selective removal or omission of insulation from the work-support bracket does not result in the reoccurrence of the condition which occasioned the need for insulation; namely, to prevent inefficient plating. It also prevents the need for oversizing of the completely insulated work-support bracket required for a given plating job because heating losses in the bracket, by virtue of the new invention, can be more readily carried away. This is of particular advantage in the case of plating light flimsy workpieces which require the utilization of mounting brackets in the form. of light springs in order to prevent distortion of the workpieces by the tension of the mounting bracket. By the efficient removal of this heat, the bracket insulation is no longer deteriorated, and the life of the fixture is greatly prolonged. Further advantages of this invention are less contamination of process solutions by chemicals from prior dips entrapped in loose insulation, greater freedom in design of the fixture, fewer production rejects, more convenient loading and unloading, and the opportunity to use chemical strippers where not previously practical because stainless steel can replace copper alloy as conducting metal in the fixture.

In the embodiment disclosed in the accompanying drawings, support bracket 26 is intended to be a rigid, nonflexible member while support bracket 28 is intended to be of flexible material having spring-type characteristics. One skilled in the art will readily perceive that various combinations of spring-type and rigid members may be used for supporting a workpiece of given configuration and that either rigid or flexible work-support pieces may have insulation selectively removed or omitted therefrom. Further, it is not necessary that there be work-support brackets attached to the frame. Instead, work-support brackets could readily be designed integrally with a frame, and therefore the frame itself might have portions of its insulation selectively removed therefrom.

I claim:

1. In an apparatus used in electrochemical processes of the type including an electrolyte solution tank, and an electrode within the tank adapted to be electrically connected to one terminal of an electric current source and adapted to extend into electrolyte solution when the tank is filled to a desired level, that improvement which comprises support means adapted to support a workpiece within the tank and adapted to be electrically connected to the other terminal of said current source and a support bracket formed of an electrically conducting metal, said support bracket having a first portion mounted on said support means and electrically connected therewith, said support bracket having a second portion spaced from the first portion adapted to be engaged with the workpiece to support the same within the tank and establish an electrical connection therewith, said support bracket having a third portion extending between and connected to said first portion and said second portion including a section of said third portion having a surface facing the electrode and adapted to be submerged when the tank is filled with solution to the desired level, insulation completely covering said surface but only partially covering the remainder of said section of said third portion so as to leave at least one uncovered area thereon where the bare metal is exposed to the surrounding medium to facilitate the transfer of heat from said metal support bracket to said medium.

2. The apparatus called for in claim 1 wherein said remainder of said section of said third portion of said support bracket has a plurality of spaced apart areas uncovered by said insulation facing in the opposite direction from said electrode.

3. The apparatus called for in claim 1 wherein said support bracket comprises a flexible metal spring.

4. The apparatus called for in claim 3 wherein said bracket comprises a generally flat spring metal strip having lengthwise opposite ends corresponding to said first and second portions a generally flat portion between the two ends adapted to be submerged when the tank is filled with solution to the desired level and having a generally flat surface facing toward said electrode and a generally flat surface facing in the opposite direction from said electrode, said insulation covering the entire flat surface facing said electrode but selectively covering the other flat surface thereof so as to leave at least one uncovered area thereon exposed to the surrounding medium to facilitate heat transfer from the strip to the medium. 

2. The apparatus called for in claim 1 wherein said remainder of said section of said third portion of said support bracket has a plurality of spaced apart areas uncovered by said insulation facing in the opposite direction from said electrode.
 3. The apparatus called for in claim 1 wherein said support bracket comprises a flexible metal spring.
 4. The apparatus called for in claim 3 wherein said bracket comprises a generally flat spring metal strip having lengthwise opposite ends corresponding to said first and second portions a generally flat portion between the two ends adapted to be submerged when the tank is filled with solution to the desired level and having a generally flat surface facing toward said electrode and a generally flat surface facing in the opposite direction from said electrode, said insulation covering the entire flat surface facing said electrode but selectively covering the other flat surface thereof so as to leave at least one uncovered area thereon exposed to the surrounding medium to facilitate heat transfer from the strip to the medium. 